This invention deals generally with hand and hoist line implements, and more specifically with an abrasion guard for "D" rings on lifting slings.
The typical end fitting on a lifting sling is a "D" ring, that is, a simple loop of metal with a somewhat triangular shape. Such a "D" ring is usually built with the base of the triangle as a straight bar and the two sides meeting at an apex which is curved to accommodate a lifting hook. The lifting sling webbing is then looped around the straight base bar of the triangle and closed by sewing.
Such lifting slings function very well for many uses, but, in some applications, particularly where the lifting sling is dragged across the ground, the floor, or the material being handled, the webbing around the straight bar is easily damaged and the useful life of the lifting sling is dramatically shortened. Because the webbing around the base bar is the thickest portion of the assembly, it is the webbing itself that is in contact with the ground or floor surface, and it is severely abraded as it is repeatedly pulled over the surface.
This problem is particularly severe for the lifting slings used in lumber sorting systems. In such equipment, the lifting sling is dragged across the floor or through the lumber at the end of each sorting cycle which accumulates a bundle of lumber. Since such sorting cycles are repeated frequently and continuously, the webbing on the "D" ring is subjected to severe abrasion, and the slings must be replaced often.
Two prior art patents have addressed the problem of external abrasion of the webbing which is wrapped around the base bar of "D" rings. U.S. Pat. No. 3,583,750 by Norton discloses a sling fitting which has a thinner cross section around which the webbing is looped, with larger cross sections on the portions of the fitting immediately adjacent to the edges of the webbing. Norton notes that this structure forms shoulders on either side of the webbing to protect the webbing from abrasion. U.S. Pat. No. 5,123,690 by Bailey discloses a wear pad which is welded to an additional bar across the "D" ring, with the wear pad protruding transverse to the webbing and thereby acting as a protective skid to hold the webbing off the surface along which it is being moved.
Both of these prior art solutions to the problem are complex and expensive. They require the construction of heavy special fittings which are structurally complex and therefore difficult and expensive to manufacture. Moreover, additional weight in a lifting fixture for a lumber sorter increases the likelihood that the fixture will damage the lumber.